Writing for the 6-member majority in Montgomery, Justice Anthony M. Kennedy stated that the 2012 decision in Miller

did more than require a sentencer to con­sider a juvenile offender’s youth before imposing life with­ out parole; it established that the penological justifications for life without parole collapse in light of ‘the distinctive attributes of youth.’ (p. 16)

As a result, he wrote, it established a “substantive rule of constitutional law,” the kind of rule that must apply even to persons whose cases otherwise would have been deemed final before the issuance of the 2012 decision.

In America, we believe in redemption. We believe, in the words of Pope Francis, that ‘every human person is endowed with an inalienable dignity, and society can only benefit from the rehabilitation of those convicted of crimes.’

We believe that when people make mistakes, they deserve the opportunity to remake their lives. And if we can give them the hope of a better future, and a way to get back on their feet, then we will leave our children with a country that is safer, stronger and worthy of our highest ideals.

A children’s day indeed.

Still, it must be noted that the solitary confinement ban applies only to the U.S. Bureau of Prisons. The DOJ report wrote at page 66:

The Department of Justice prosecutes very few juveniles, and so the Bureau is only responsible for the custody of a very small number of juveniles. As of December 5, 2015, the Bureau was responsible for 71 juvenile inmates, of which 45 were serving a term of incarceration, and 26 were under the supervision of the U.S. Probation Office.

Many thousands are in state correctional systems, and thus not affected by Obama’s decision.

And there is much yet to be done of a preventive nature, to help children from entering the juvenile justice system at all.